Filler for paper making process

ABSTRACT

The present invention relates to a filler comprising clay and cellulose derivative having a degree of substitution of net ionic groups up to about 0.65.

This application is a divisional application of U.S. patent applicationSer. No. 11/149,613, filed Jun. 10, 2005, now U.S. Pat. No. 8,252,143,and claims priority to U.S. Provisional Patent Application 60/581,784,filed Jun. 22, 2004, the contents of all of which above-listedapplications are incorporated by reference herein, in their entireties.

The present invention relates to a filler comprising clay and cellulosederivative. The invention further relates to a method of making thefiller, the use of the filler in papermaking, a process for papermakingin which the filler is used as an additive as well as paper comprisingthe filler.

BACKGROUND OF THE INVENTION

In the production of filled paper, an aqueous suspension containingcellulosic fibres, fillers and additives, referred to as the stock, isfed into a headbox which ejects the stock onto a forming wire. Water isdrained from the stock through the forming wire so that a wet web ofpaper is formed on the wire, and the web is further dewatered and driedin the drying section of the paper machine.

Highly filled paper is an established trend in the paper industry, notonly, due to the savings in the decreased use of fibre, but also due toimproved product quality, such as higher opacity and betterprintability. For super calandered paper (SC paper) and many papergrades containing mechanical fibres, kaolin clay is the most commonlyused filler. The clay particles have a flake or plate shape, and atcalandering the flakes are uniformly oriented, giving a high gloss andsmoothness to the paper. The amount of filler can be as high as 30% ormore.

A high degree of filler causes a decrease in paper strength as well astinting and dusting. A rule of thumb at filler usage in paper is that a10% increase in filler content decreases the strength by 20%. Problemswith linting and dusting occur, as small fibre fragments and fillers arenot properly bound into the paper. This can give a specific problem atrotogravure printing of SC paper, called missing dots, when ink ismissing in dots in the print.

Addition of a binding agent can increase the strength of the paper aswell as decrease the tinting and dusting. Among other materials starchhas been used as a binding agent. However, in SC paper making, thecalandering of the paper is done at a load of 100-350 kN/m. Starch makesthe paper brittle and it can break at such heavy loads. Starch alsomakes the paper denser already prior to calandering. Therefore, nostarch or small additions (1-2 kg/tonne dry paper) is used in SC papermaking.

Conventional CMC is sometimes added to the wet end as a strengthadditive. However, then the problem is that dewatering is slowed downconsiderably. A third possibility, synthetic strength additives, can beused but they are often quite expensive.

For all paper grades with high filler loadings, paper strength, drainageand filler retention are important issues. Sometimes size is added, andthen also size consumption is higher when the filler loadings areincreased and/or when starch is not used.

U.S. Pat. No. 5,759,346 describes a method of improving strength andreducing lint and dust in the production of tissue paper. The filler isa kaolin clay which has been pre-treated with a cationic starch.

WO 01/86067 describes a method for pre-treating a filler with ahydrophobic polymer, which is a synthetic polymer comprising acrylateand styrene monomers. The use of the pre-treated filler improves wetstrength and reduces the linting of the paper.

Furthermore, WO 95/13324 refers to calcium carbonate treated with acellulose derivative such as sodium carboxymethyl cellulose (“CMC”)having a degree of substitution of 0.70. Said treated calcium carbonateis used as filler in alkaline papermaking suspensions whereby thebrightness of the paper is increased.

There is still need for a filler which provides an improved papermakingprocess and better properties of the paper produced. It would be desiredto provide a filler which renders possible production of highly filledpaper showing excellent printing and mechanical properties. It wouldalso be desirable to provide a filler which is compatible with drainageand retention aids, and hereby leads to good drainage, retention andpaper machine runnability. It would also be desirable to provide asimple and efficient process for producing a filler showing the abovecharacteristics.

SUMMARY OF THE INVENTION

The present invention generally relates to a filler comprising clay andcellulose derivative. The present invention further generally relates toa filler comprising clay and carboxymethyl cellulose derivate. Thepresent invention also generally relates to a method of making thefiller by mixing clay with a cellulose derivative, the use of the filleras an additive in papermaking as well as paper comprising the filler.The invention further generally relates to papermaking process in whichthe filler is introduced into an aqueous cellulosic suspension.

More specifically, the invention relates to a filler comprising clay anda cellulose derivative having a degree of substitution of net anionicgroups up to about 0.65. The invention also relates to a fillercomprising clay and a cellulose derivative having a degree ofsubstitution of carboxyalkyl groups up to about 0.65. The inventionfurther relates to a method of producing a filler which comprises mixingclay with a cellulose derivative having a degree of substitution of netionic groups up to about 0.65. The invention also relates to a method ofproducing a filler which comprises mixing clay with a cellulosederivative having a degree of substitution of carboxyalkyl groups up toabout 0.65. The invention further relates to a filler obtainable bythese methods. The invention further relates to a papermaking processwhich comprises providing an aqueous suspension containing cellulosicfibres, introducing into the suspension a filler comprising clay andcellulose derivative having a degree of substitution of net ionic groupsup to about 0.65, and dewatering the suspension to form a web or sheetof paper. The invention also relates to a papermaking process whichcomprises providing an aqueous suspension containing cellulosic fibres,introducing into the suspension a filler comprising clay and cellulosederivative having a degree of substitution of carboxyalkyl groups up toabout 0.65, and dewatering the suspension to form a web or sheet ofpaper. In the papermaking process, the filler can be introduced into thecellulosic suspension by adding the clay and cellulose derivativeseparately or together as a single composition.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a new filler that is suitably for use inpapermaking. It has surprisingly been found that the filler according tothe invention makes it possible to reduce some of the problemsassociated with fillers commonly used in papermaking and incorporated inpaper. More specifically, by employing the filler of this invention inpapermaking processes it is possible to reduce the linting and dustingof paper and provide paper with excellent printing and mechanicalproperties. Additional advantages shown by the present invention includegood and/or improved dewatering and fines retention, which leads tobenefits in terms of paper machine runnability.

When using the filler in the making of SC paper and newsprint paper ithas been observed that the present invention makes it possible to reducethe linting and dusting of the paper without adversely affecting themechanical properties of the paper produced and without decreasing thedewatering and retention of fines and filler in the papermaking process.

According to the present invention it has been observed that thecellulose derivative can be mixed with and more effectively be adsorbedon or attached to the clay surface during simple processing. The fillerof the invention can be regarded as a modified filler, or cellulosederivative-treated filler.

According to the present invention it has been found that very goodresults can be obtained by adding the clay and cellulose derivative to acellulosic suspension either separately or together in a pre-mixed orpre-treated form. The pre-treatment of the clay with the cellulosederivative provides a convenient way of separately processing only onecomponent of the cellulosic suspension to produce a modified filler,which can be used instead of or partly replacing conventional fillers.Without being bound to any theory, it is believed that cellulosederivative is adsorbed to the clay when mixing the components, whichadsorption may also take place in situ in the cellulosic suspension whenseparately adding the components.

The filler according to the invention comprises a clay and a cellulosederivative. Examples of suitable clays include those having a flake orplate like shape. Examples of suitable clays include talc, hydrotalcit,kaolin, calcinated clay, bentonite or mixtures thereof, preferablykaolin, calcinated clay or talc, most preferably kaolin and calcinatedclay. Examples of suitable clays include those having a specific surfacearea in the range from about 2 m²/g to about 800 m²/g, suitably fromabout 2 m²/g to about 600 m²/g, most preferably from about 5 m²/g toabout 20 m²/g. The particle size is usually from about 0.1 μm to about50 μm, preferably from about 0.1 μm to about 5 μm and most preferablyfrom about 0.8 μm to about 3 μm.

Natural kaolin clay has the chemical formula Al₂O₃*2SiO₂*2H₂O. Kaolinclays include so called dioctahedral 1:1 aluminium silicates. The kaolinclay usually have a particle size of from about 1 μm to about 5 μm,preferably from about 1 μm to about 3 μm. The kaolin clay usually has asurface area of from about 3 m²/g to about 10 m²/g, suitably from about5 m²/g to about 8 m²/g.

Calcinated clay has the formula Al₂O₃*SiO₂. The calcinated clay usuallyhas a specific surface area of from about 10 m²/g to about 20 m²/g,suitably from about 15 m²/g to about 17 m²/g. The calcinated clayusually has a particle size in the range of from about 0.8 μm to about 4μm, preferably from about 0.8 μm to about 2 μm.

The filler according to the invention further comprises a cellulosederivative. It is preferred that the cellulose derivative iswater-soluble or at least partly water-soluble or water-dispersible,preferably water-soluble or at least partly water-soluble. Preferably,the cellulose derivative is ionic. The cellulose derivative can beanionic, cationic or amphoteric, preferably anionic or amphoteric.Examples of suitable cellulose derivatives include cellulose ethers,e.g. anionic and amphoteric cellulose ethers, preferably anioniccellulose ethers. The cellulose derivative preferably has ionic orcharged groups, or substituents. Examples of suitable ionic groupsinclude anionic and cationic groups. Examples of suitable anionic groupsinclude carboxylate, e.g. carboxyalkyl, sulphonate, e.g. sulphoalkyl,phosphate and phosphonate groups in which the alkyl group can be methyl,ethyl propyl and mixtures thereof, suitably methyl; suitably thecellulose derivative contains an anionic group comprising a carboxylategroup, e.g. a carboxyalkyl group. The counter-ion of the anionic groupis usually an alkali metal or alkaline earth metal, suitably sodium.

Examples of suitable cationic groups of cellulose derivatives accordingto the invention include salts of amines, suitably salts of tertiaryamines, and quaternary ammonium groups, preferably quaternary ammoniumgroups. The substituents attached to the nitrogen atom of amines andquaternary ammonium groups can be same or different and can be selectedfrom alkyl, cycloalkyl, and alkoxyalkyl, groups, and one, two or more ofthe substituents together with the nitrogen atom can form a heterocyclicring. The substituents independently of each other usually comprise from1 to about 24 carbon atoms, preferably from 1 to about 8 carbon atoms.The nitrogen of the cationic group can be attached to the cellulose orderivative thereof by means of a chain of atoms which suitably comprisescarbon and hydrogen atoms, and optionally O and/or N atoms. Usually thechain of atoms is an alkylene group with from 2 to 18 and suitably 2 to8 carbon atoms, optionally interrupted or substituted by one or moreheteroatoms, e.g. O or N such as alkyleneoxy group or hydroxy propylenegroup. Preferred cellulose derivatives containing cationic groupsinclude those obtained by reacting cellulose or derivative thereof witha quaternization agent selected from 2,3-epoxypropyl trimethyl ammoniumchloride, 3-chloro-2-hydroxypropyl trimethyl ammonium chloride andmixtures thereof.

The cellulose derivatives of this invention can contain non-ionic groupssuch as alkyl or hydroxy alkyl groups, e.g. hydroxymethyl, hydroxyethyl,hydroxypropyl, hydroxybutyl and mixtures thereof, e.g. hydroxyethylmethyl, hydroxypropyl methyl, hydroxybutyl methyl, hydroxyethyl ethyl,hydroxypropoyl and the like. In a preferred embodiment of the invention,the cellulose derivative contains both ionic groups and non-ionicgroups.

Examples of suitable cellulose derivatives according to the inventioninclude carboxyalkyl celluloses, e.g. carboxymethyl cellulose,carboxyethyl cellulose, carboxypropyl cellulose, sulphoethylcarboxymethyl cellulose, carboxymethyl hydroxyethyl cellulose(“CM-HEC”), carboxymethyl cellulose wherein the cellulose is substitutedwith one or more non-ionic substituents, preferably carboxymethylcellulose (“CMC”). Examples of suitable cellulose derivatives andmethods for their preparation include those disclosed in U.S. Pat. No.4,940,785, which is hereby incorporated herein by reference.

The terms “degree of substitution” or “DS”, as used herein, mean thenumber of substituted ring sites of the beta-anhydroglucose rings of thecellulose derivative. Since there are three hydroxyl groups on eachanhydroglucose ring of the cellulose that are available forsubstitution, the maximum value of DS is 3.0. According to one preferredembodiment of the invention, the cellulose derivative has a degree ofsubstitution of net ionic groups (“DS_(NI)”) up to about 0.65, i.e. thecellulose derivative has an average degree of net ionic substitution perglucose unit up to about 0.65. The net ionic substitution can be netanionic, net cationic or net neutral. When the net ionic substitution isnet anionic, there is a net excess of anionic groups (net anionicgroups=the average number of anionic groups minus the average number ofcationic groups, if any, per glucose unit) and DS_(NI) is the same asthe degree of substitution of net anionic groups (“DS_(NA)”). When thenet ionic substitution is net cationic, there is a net excess ofcationic groups (net cationic groups=the average number of cationicgroups minus the average number of anionic groups, if any, per glucoseunit) and DS_(NI) is the same as the degree of substitution of netcationic groups (“DS_(NC)”). When the net ionic substitution is netneutral, the average number of anionic and cationic groups, if any, perglucose unit is the same, and DS_(NI) as well as DS_(NA) and DS_(NC) are0. According to another preferred embodiment of the invention, thecellulose derivative has a degree of substitution of carboxyalkyl groups(“DS_(CA)”) up to about 0.65, i.e. the cellulose derivative has anaverage degree of carboxyalkyl substitution per glucose unit up to about0.65. The carboxyalkyl groups are suitably carboxymethyl groups and thenDS_(CA) referred to herein is the same as the degree of substitution ofcarboxymethyl groups (“DS_(CM)”). According to these embodiments of theinvention, DS_(NI), DS_(NA), DS_(NC) and DS_(CA) independently of eachother are usually up to about 0.60, suitably up to about 0.50,preferably up to about 0.45 and more preferably up to 0.40, whereasDS_(NI), DS_(NA), DS_(NC) and DS_(CA) independently of each other areusually at least 0.01, suitably at least about 0.05, preferably at leastabout 0.10 and more preferably at least about 0.15. The ranges ofDS_(NI), DS_(NA), DS_(NC) and DS_(CA) independently of each other areusually from about 0.01 to about 0.60, suitably from about 0.05 to about0.50, preferably from about 0.10 to about 0.45 and more preferably fromabout 0.15 to about 0.40.

Cellulose derivatives that are anionic or amphoteric usually have adegree of anionic substitution (“DS_(A)”) in the range of from 0.01 toabout 1.0 as long as DS_(NI) and DS_(NA) are as defined herein; suitablyfrom about 0.05, preferably from about 0.10, and more preferably fromabout 0.15 and suitably up to about 0.75, preferably up to about 0.5,and more preferably up to about 0.4. Cellulose derivatives that arecationic or amphoteric can have a degree of cationic substitution(“DS_(C)”) in the range of from 0.01 to about 1.0 as long as DS_(NI) andDS_(NC) are as defined herein; suitably from about 0.02, preferably fromabout 0.03, and more preferably from about 0.05 and suitably up to about0.75, preferably up to about 0.5, and more preferably up to about 0.4.The cationic groups are suitably quaternary ammonium groups and thenDS_(C) referred to herein is the same as the degree of substitution ofquaternary ammonium groups (“DS_(QN)”). For amphoteric cellulosederivatives of this invention DS_(A) or DS_(C) can of course be higherthan 0.65 as long as DS_(NA) and DS_(NC), respectively, are as definedherein. For example, if DS_(A) is 0.75 and DS_(C) is 0.15, then DS_(NA)is 0.60.

Examples of suitable cellulose derivatives having degrees ofsubstitution as defined above include the water-soluble low DScarboxyalkyl cellulose derivatives. The water-soluble cellulosederivatives suitably has a solubility of at least 85% by weight, basedon total weight of dry cellulose derivative, in an aqueous solution,preferably at least 90% by weight, more preferably at least 95% byweight, and most preferably at least 98% by weight.

The cellulose derivative usually has an average molecular weight whichis at least 20,000 Dalton, preferably at least 50,000 Dalton, and theaverage molecular weight is usually up to 1,000,000 Dalton, preferablyup to 500,000 Dalton.

Preferably, in the filler according to the invention, the cellulosederivative is at least in part adsorbed on or attached to the clay.Suitably, at least about 10% by weight, preferably at least about 30% byweight, more preferably at least about 45% by weight and most preferablyat least about 60% by weight of the cellulose derivate is adsorbed on orattached to the clay.

The filler according to the invention usually has a clay content of atleast 0.0001% by weight; the clay content can be from about 0.0001 toabout 99.5% by weight, suitably from about 0.1 to about 90% by weight,and preferably from about 60 to about 80% by weight, based on the weightof the solids of the filler, i.e. based on the dry weight of the filler.The filler usually has a cellulose derivative content of at least 0.01%by weight; the cellulose derivative content can be from about 0.01 toabout 30% by weight, suitably from about 0.1 to about 20% by weight, andpreferably from about 0.3 to about 10% by weight, based on the weight ofthe solids of the filler.

The filler according to the invention can be supplied as a solidmaterial that can be essentially free of water. It can also be suppliedas an aqueous composition. The content of aqueous phase, or water, canvary within wide limits, depending on the method of production andintended use.

The present invention also relates to a method of making a filler whichcomprises mixing a cellulose derivative, e.g. any one of the cellulosederivatives defined herein, with clay. The cellulose derivative and clayare suitably used in amounts so as to provide a filler according to theinvention having contents of cellulose derivative and clay as definedherein.

The cellulose derivative and clay used can be present as solids or inaqueous compositions, and mixtures thereof. The clay is suitably presentas a finely divided material. The mixing can be achieved by adding thecellulose derivative to the filler, or vice versa, in a batch,semi-batch or continuous process. According to a preferred embodiment ofthe invention, the cellulose derivative is added as a solid to anaqueous composition of the clay and the composition obtained is thensuitably subjected to effective dispersing to dissolve the cellulosederivative. Preferably, the mixing is carried out by first forming aneutral to alkaline aqueous phase, suitably an aqueous solution, ofcellulose derivative which is then mixed with an aqueous composition ofclay. Prior to mixing with the clay, the aqueous phase of cellulosederivative can be subjected to pre-treatment, e.g. homogenisation,centrifugation and/or filtration, for example for separating undissolvedcellulose derivative, if any, from the aqueous phase.

Preferably, the cellulose derivative is mixed with the clay to allow atleast part of the cellulose derivative to adsorb on or attach to theclay, preferably so that it is hardly removed from the material bydilution with water. This can be accomplished by carrying out mixingunder a period of time that is sufficient long to allow the adsorptionon attachment. Suitably the mixing time is at least about 1 min,preferably at least about 5 min, more preferably at least about 10 minand most preferably at least about 20 min. Mixing periods of evenseveral hours (1-10 h) are possible if it is desired to reach a highdegree of attachment. Suitably, at least about 10% by weight, preferablyat least about 30% by weight, more preferably at least about 45% byweight and most preferably at least about 60% by weight of the cellulosederivate is transferred from the aqueous phase and adsorbed on orattached to the clay or other components present in the clay.

The pH of the aqueous phase of cellulose derivative is usually adjustedfor sorption of the specific cellulose derivative used at a value fromabout 4 to about 13, preferably from about 6 to about 10, morepreferably from about 7 to about 8.5. A suitable base or acid can beused for adjusting the pH. Examples of suitable bases includebicarbonates and carbonates of alkali metals and alkali metalhydroxides, suitably sodium bicarbonate, sodium carbonate and sodiumhydroxide. Examples of suitable acids include mineral acids, organicacids and acid salts, suitably sulphuric acid and its acid salts, suchas alum. In general, at a lower pH, i.e. a pH from about 4.0 to neutral,adsorption of the cellulose derivative is higher but solubility isdecreased, whereas at higher pH the adsorption is reduced but solubilityis increased.

The temperature is not critical; in operations in non-pressurizedconditions the temperature is typically from about 10 to about 100° C.,preferably from about 20 to about 80° C. However, higher temperaturesare more favourable, suitably the temperature of the aqueous compositionduring mixing is from about 30 up to about 70° C., more preferably fromabout 40 up to about 60° C.

The filler obtained by the method of the invention can be used as such,for example in papermaking. If present as an aqueous composition, it canbe used directly or it can be dried, if desired, for example to simplifyshipping.

The present invention also relates to a process for the production ofpaper which comprises providing an aqueous suspension containingcellulosic fibres (“cellulosic suspension”), introducing into thecellulosic suspension a filler, e.g. any one of the fillers definedherein, and dewatering the cellulosic suspension to form a web or sheetof paper. Preferably, the filler is introduced into the cellulosicsuspension by adding it as a single composition. Alternatively, the clayand cellulose derivative (e.g. any one of the cellulose derivativesdefined herein) can be separately added to the cellulosic suspension andthe filler is formed in situ in the cellulosic suspension.

The filler according to the invention can be added to the cellulosicsuspension in amounts which can vary within wide limits depending on,inter alia, type of cellulosic suspension, type of paper produced, pointof addition, etc. The filler is usually added in an amount within therange of from 1 to about 50% by weight, suitably from about 5 to about40% by weight, and usually from about 10 to about 30% by weight, basedon the weight of dry fibres. Accordingly, the paper according to theinvention usually has a content of filler of this invention within therange of from 1 to about 50% by weight, suitably from about 5 to about40% by weight, and usually from about 10 to about 30% by weight, basedon the weight of dry fibres.

In the process, other components may of course be introduced into thecellulosic suspension. Examples of such components include conventionalfillers, optical brightening agents, sizing agents, coagulantflocculants, drainage and retention aids, dry strength agents, wetstrength agents, etc. Examples of suitable conventional fillers includekaolin, china clay, titanium dioxide, gypsum, talc, natural andsynthetic calcium carbonates, e.g. chalk, ground marble and precipitatedcalcium carbonate, hydrogenated aluminum oxides (aluminumtrihydroxides), calcium sulphate, barium sulphate, calcium oxalate, etc.When using the filler according to the invention together withconventional filler, the filler according to the invention can bepresent in an amount of at least 1% by weight, suitably at least 5% byweight, preferably at least 10% by weight, more preferable at leastabout 20% by weight, and suitably up to about 99% by weight, based onthe dry weight of all fillers. Examples of suitable sizing agentsinclude non-cellulose-reactive sizing agents, e.g. rosin-based sizingagents like rosin-based soaps, rosin-based emulsions/dispersions, andcellulose-reactive sizing agents, e.g. emulsions/dispersions of acidanhydrides like alkenyl succinic anhydrides (ASA), alkenyl and alkylketene dimers (AKD) and multimers. Examples of suitable drainage andretention'aids include organic polymeric products, e.g. cationic,anionic and non-ionic polymers including cationic polyethylene imines,cationic, anionic and non-ionic polyacrylamides, cationic polyamines,cationic starch, and cationic guar; inorganic materials, e.g. aluminiumcompounds, anionic microparticulate materials like colloidalsilica-based particles, clays of smectite type, e.g. bentonite,montmorillonite; colloidal alumina, and combinations thereof. Examplesof suitable combinations of drainage and retention aids include cationicpolymers and anionic microparticulate materials, e.g. cationic starchand anionic colloidal silica-based particles, cationic polyacrylamideand anionic colloidal silica-based particles as well as cationicpolyacrylamide and bentonite or montmorillonite. Examples of suitablewet strength agents include polyamines and polyaminoamides. Papercontaining filler according to the invention and cationic starch showsvery good strength properties.

The term “paper”, as used herein, include not only paper and theproduction thereof, but also other cellulosic fibre-containing sheet orweb-like products, such as for example board and paperboard, and theproduction thereof. The process can be used in the production of paperfrom different types of aqueous suspensions of cellulosic(cellulose-containing) fibres and the suspensions should suitablycontain at least 25% by weight and preferably at least 50% by weight ofsuch fibres, based on a dry substance. The cellulosic fibres can bebased on virgin fibres and/or recycled fibres, including fibres of woodor annual or perennial plants. The cellulosic suspension can bewood-containing or wood-free, and it can be based on fibres fromchemical pulp such as sulphate, sulphite and organosolve pulps,mechanical pulp such as thermo-mechanical pulp, chemo-thermo-mechanicalpulp, refiner pulp and ground wood pulp, from both hardwood andsoftwood, and can also be based on recycled fibres, optionally fromde-inked pulps, and mixtures thereof. The cellulosic suspension suitablyhas a pH in the acid to neutral to alkaline range, e.g. from about 4 toabout 10, preferably from about 5 to about 8.

The invention is further illustrated in the following Examples which,however, are not intended to limit the same. Parts and % relates toparts by weight and % by weight, respectively, unless otherwise stated.

EXAMPLE 1

Fillers according to the invention have been prepared by treating claywith cellulose derivatives. Cellulose derivatives used werecarboxymethyl cellulose (“CMC”) and quaternary ammonium carboxymethylcellulose (“QN-CMC”). The mole weight of the CMC was <200,000 Dalton.The clay used in the examples was kaolin clay.

The types of CMC used to treat the clay were the following:

CMC 0.35 DS_(CA) = 0.35 CMC 0.5 Gabrosa PA 947 Akzo Nobel DS_(CA) = 0.5QN-CMC DS_(CA) = 0.4 and DS_(QN) = 0.17

Preparation of CMC-Modified Clay:

CMC was first dissolved into water to a consistency of 0.5% by weight.Thereafter, the CMC composition was added to the clay filler slurry andmixed during 35 to 40 minutes at a temperature of about 50° C.

EXAMPLE 2

In the following example, SC paper (super calandered) was prepared usingkaolin clay treated with carboxymethyl cellulose (CMC). The CMC used wasQN-CMC and CMC 0.5 according to the present invention as described inExample 1. The preparation of the CMC-modified clay has been done asdescribed in Example 1. The SC paper was then tested for ash content,total retention and linting.

The paper sheets were produced from a SC pulp furnish consisting of 80%mechanical pulp and 20% chemical pulp. The furnish suspension contained50% clay filler, had a consistency of 0.5% by weight, pH of 7.7 and aconductivity of 0.3 mS/cm. To the pulp suspension or to the clay slurryan amount of 2% CMC/tonne dry clay was added. A retention systemcontaining cationic polymer (Eka retention polymer PL 1510) and silicaparticles (Eka retention silica NP 442) was also added. Both the polymerand silica particles were added in an amount of 0.2 kg/tonne dry fibres.The addition sequence was the following:

Addition of separate CMC when used: 0 sec. Addition of filler: 15 sec.Addition of retention polymer: 30 sec. Addition of retention silica: 45sec. Sheet making: 105 sec.

The paper sheets prepared in the following examples were made accordingto standard using a Dynamical Sheet Former (“Formette”, CTP Grenoble).

The paper sheets were tested for retention and ash content, see table 1.Separate CMC 0.5 means that the CMC 0.5 was added before the untreatedclay.

TABLE 1 Test Type of CMC and Ash level Total retention No. addition [%][%] 1 QN-CMC on clay 39.8 83.0 2 CMC 0.5 on clay 34.2 76.0 3 SeparateCMC 0.5 36.1 78.2

The sheets were also tested for linting, see table 2. Linting ismeasured by applying a well defined adhesive tape to an area of thepaper surface and then mechanically draw off the tape at a specificforce and angle. The amount of lint, fibre fragments and filler, presenton the tape is then measured. This measurement was also made aftercalandering the paper sheets.

TABLE 2 Test Type of CMC and Linting [mg] Linting [mg] No. addition Nocalandering After calandering 1 QN-CMC on clay 2.5 4.5 2 CMC 0.5 on clay4.2 9.4 3 Separate CMC 0.5 4.3 10.0

EXAMPLE 3

In this example, newsprint paper was prepared using a clay treated withCMC. The CMC used was CMC 0.35 and CMC 0.5 as defined in example 1. Theclay used was a kaolin clay. The preparation of the CMC-modified clay habeen done as described in Example 1. Tensile strength index was measuredon the paper and the results are displayed in table 3.

Paper sheets were produced from a newsprint pulp furnish consisting of75% mechanical pulp and 25% de-inked newsprint pulp. The furnishsuspension contained 10% calcinated clay filler, had a consistency of0.3%, pH of 7.2 and conductivity of 1.0 mS/cm. To the pulp suspension orto the clay slurry an amount of 2% CMC/tonne dry clay was added. Theaddition sequence was the following:

Addition of separate CMC when used: 0 sec. Addition of filler: 15 sec.Sheet making: 105 sec.

The paper sheets prepared in the following examples were made accordingto standard using a Dynamical Sheet Former (“Formette”, CTP Grenoble).

Separate CMC 0.5 means that the CMC 0.5 was added before the untreatedclay.

TABLE 3 Test No. Type of CMC and addition Tensile index [kNm/kg] 1 CMC0.35 on clay 31.5 2 CMC 0.5 on clay 29.3 3 Separate CMC 0.5 29.6

EXAMPLE 4

A SC paper furnish was prepared using a clay treated with CMC. Threedifferent kinds of CMC were used to prepare the filler, CMC 0.35, CMC0.5 and QNC-CMC according to the present invention. The types of CMC areas defined in example 1. The preparation of the CMC-modified clay havebeen done as described in Example 1, but the CMC and clay filler slurryhas been mixed for 15 minutes or 4 hours respectively.

The SC paper furnish that was used consisted of 80% mechanical pulp and20% chemical pulp. The furnish suspension contained 50% clay filler, hada consistency of 0.25%, pH of 7.8 and conductivity of 0.3 mS/cm. To theclay slurry an amount of 2% CMC/tonne dry clay was added and to the pulpsuspension a retention system containing cationic polymer (Eka retentionpolymer PL 1510) and silica particles (Eka retention silica NP 780) wasadded. Both the polymer and silica particles were added in an amount of1 kg/tonne dry fibres. The addition sequence was the following:

Addition of CMC treated filler:  0 sec. Addition of retention polymer:15 sec. Addition of retention silica: 30 sec. Dewatering: 45 sec.

The dewatering values are presented in table 4.

TABLE 4 Pre-treatment of Pre-treatment of Test Type of filler for 4hours filler for 15 minutes No. CMC Dewatering time (s) Dewatering time(s) 1 CMC 0.35 45.0 48.8 2 QN-CMC 40.4 33.0 3 CMC 0.5 64.7 58.7

The invention claimed is:
 1. A filler composition consisting essentiallyof water, a clay selected from the group consisting of talc,hydrotalcite, kaolin, calcinated clay, bentonite and mixtures thereof,and an anionic cellulose derivative containing one or more carboxymethylgroups and having a degree of substitution of carboxymethyl groups fromabout 0.15 up to about 0.40, and said filler composition has a cellulosederivative content from 0.3 to 10% by weight, based on the weight of thesolids of the filler.
 2. The filler composition according to claim 1,wherein the degree of substitution is from about 0.15 up to about 0.35.3. The filler composition according to claim 1, wherein the filler has aclay content from 60 to about 80% by weight, based on the weight of thesolids of the filler.
 4. The filler composition according to claim 1,wherein the clay is kaolin.
 5. A filler composition comprising clayselected from the group consisting of talc, hydrotalcite, kaolin,calcinated clay, bentonite, and mixture thereof; and an anioniccellulose derivative having a degree of substitution of caboxymethylgroups from about 0.15 up to about 0.40, wherein said clay has beenmodified by said cellulose derivative, and said filler composition has acellulose derivative content from 0.3 to 10% by weight, based on theweight of the solids of the filler.
 6. The filler composition accordingto claim 5, wherein the degree of substitution is from about 0.15 up toabout 0.35.
 7. The filler composition according to claim 5, wherein thefiller has a clay content from 60 to about 80% by weight, based on theweight of the solids of the filler.
 8. The filler composition accordingto claim 5, wherein the clay is kaolin.